全文获取类型
收费全文 | 102篇 |
免费 | 5篇 |
出版年
2021年 | 2篇 |
2018年 | 2篇 |
2016年 | 1篇 |
2015年 | 2篇 |
2013年 | 7篇 |
2012年 | 5篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 2篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 6篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 2篇 |
2002年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 4篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1988年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1977年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有107条查询结果,搜索用时 15 毫秒
31.
ABSTRACT The acoustic characteristics of an Amazonian lowland rain forest study site in southern Venezuela was analysed to determine environmental constraints upon acoustic communication. Signal degradation was measured by conducting transmission experiments at different heights above ground level. Measurements of ambient noise served to determine possible communication distances for various times of day, heights above ground level and frequencies. “Sound windows” for acoustic long-range communication were found for low frequencies, calling heights in the midstorey and calling in the morning or during the night. Sound attenuation was affected by height and frequency but not by time of day. Background noise varied remarkably with time of day and frequency and had a greater impact on communication distance than signal attenuation. 相似文献
32.
Organismic diversity, as well as distributional and ecological patterns, can be fully understood in an evolutionary framework only. Reliable phylogenetic trees are required to ‘read history’, but are not yet available for most marine invertebrate groups. Molecular systematics offers an enormous potential, but still fails for ‘all‐species approaches’ on groups with species that are rare or occur in remote areas only, simply because there is no easily collectable material available for sequence analyses. Exploring morphologically aberrant corambid nudibranch gastropods as a case study, we assess whether or not morphology‐based phylogenetic analyses can fill this gap and produce a tree that allows a detailed view on evolutionary history. Morphology‐based parsimony analysis of corambids and potential relatives resulted in a well‐resolved and remarkably robust topology. As an offshoot of kelp‐associated onchidoridid ancestors, and obviously driven by the heterochronic shortening of life cycles and morphological juvenilization in an ephemeral habitat, the ancestor of corambids originated in cool northern Pacific coastal waters. A basal clade (the genus Loy) diverged there, adapting to live on soft bottoms under successive reversals of paedomorphic traits. The more speciose Corambe lineage radiated preying upon short‐lived encrusting bryozoa in a high‐energy kelp environment. Selection favoured transformation of the mantle into a cuticle‐covered shield, and successive paedomorphic translocations of dorid anal gills to the protected ventral side of the body, where compensatory, multiple gills evolved. Corambe species probably first colonized tropical American seas, and then radiated in worldwide temperate waters: this is explained by the excellent long‐distance dispersal abilities afforded by rafting on kelp, with the subsequent divergence of colonizers in allopatry. The competitive coexistence of Corambe pacifica MacFarland & O'Donoghue, 1929 and Corambe steinbergae (Lance, 1962) off California is the result of independent colonization events. The closing of the Isthmus of Panama separated the latter species from a flock that have radiated within warm Atlantic waters since then. Our case study shows that morphological structures, if investigated in depth, bear the potential for an efficient phylogenetic analysis of groups that are still elusive to molecular analyses. Tracing character evolution and integrating a wide range of geographic, biological, and ecological background information allowed us to reconstruct an evolutionary scenario for corambids that is detailed and plausible, and can be tested by future molecular approaches. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 163 , 585–604. 相似文献
33.
Y Deng J Zhao D Sakurai KM Kaufman JC Edberg RP Kimberly DL Kamen GS Gilkeson CO Jacob RH Scofield CD Langefeld JA Kelly ME Alarcón-Riquelme BIOLUPUS GENLES Networks JB Harley TJ Vyse BI Freedman PM Gaffney KM Sivils JA James TB Niewold RM Cantor W Chen BH Hahn EE Brown PROFILE BP Tsao 《Arthritis research & therapy》2012,14(Z3):A5
34.
35.
The species Hebeloma vesterholtii spec. nov. is described. It is morphologically and molecularly closely related to Hebeloma theobrominum from which it can be distinguished using either morphological or molecular characters. Both of these species belong to section Theobromina. The new species is known from 13 collections from six European countries. 相似文献
36.
Horizontal transmission, vertical inactivation, and stochastic loss of mariner-like transposable elements 总被引:13,自引:5,他引:8
Horizontal transmission has been well documented as a major mechanism for
the dissemination of mariner-like elements (MLEs) among species. Less well
understood are mechanisms that limit vertical transmission of MLEs
resulting in the "spotty" or discontinuous distribution observed in closely
related species. In this article we present evidence that the genome of the
common ancestor of the melanogaster species subgroup of Drosophila
contained an MLE related to the mellifera (honey bee) subfamily. Horizontal
transmission, approximately 3-10 MYA, is strongly suggested by the
observation that the sequence of the MLE in Drosophila erecta is 97%
identical in nucleotide sequence with that of an MLE in the cat flea,
Ctenocephalides felis. The D. erecta MLE has a spotty distribution among
species in the melanogaster subgroup. The element has a high copy number in
D. erecta and D. orena, a moderate copy number in D. teissieri and D.
yakuba, and was apparently lost ("stochastic loss") in the lineage leading
to D. melanogaster, D. simulans, D. mauritiana, and D. sechellia. In D.
erecta, most copies are concentrated in the heterochromatin. Two copies
from D. erecta, denoted De12 and De19, were cloned and sequenced, and they
appear to be nonfunctional ("vertical inactivation"). It therefore appears
that the predominant mode of MLE evolution is vertical inactivation and
stochastic loss balanced against occasional reinvasion of lineages by
horizontal transmission.
相似文献
37.
M. J. Beker J. E. Blumbergs E. J. Ventina A. I. Rapoport 《Applied microbiology and biotechnology》1984,19(5):347-352
Summary This paper describes the characteristics of the structural and functional organization of cellular membranes rehydrated after dehydration of the yeast Saccharomyces cerevisiae. It was noted that dehydration and subsequent rehydration of yeast cells causes a considerable increase of cytoplasmic membrane permeability. Addition of CaCl2, glucose and polyethyleneglycol to the rehydration medium caused a decrease in cell permeability, assessed as the losses of potassium ions, nucleotides, as well as the total losses of intracellular compounds. KCl had a positive effect only at concentrations above 10%. Yeast cells, dried to residual moisture lower than 20%, showed a decrease in membrane permeability as temperatures of the rehydration medium increased up to 38°–43°C. Upon reactivation of viable dehydrated cells in a nutrient medium, a reparation of the structural damages of various intracellular membranes takes place. It was established that at cell dehydration to residual moistures of 8%–12% all the free and a part of bound water is evaporated from cells. 相似文献
38.
P B Zikmanis L P Auzinia R V Kruche M V Margevicha S I Auzan M E Beker 《Mikrobiologiia》1989,58(3):471-474
The resistance of a Saccharomyces cerevisiae population against gamma-irradiation (400 krd), heating (60 degrees C), repeated freezing--thawing and rehydration of dehydrated cells was shown to depend on the density of a cell suspension. The percentage of damaged cells (stained with primulin) was found to increase in a suspension with decreasing cell concentrations. The effect was also exerted in an oxygen-free medium. The percentage of undamaged cells increased in populations with a lower cell concentration when a more viscous medium (0.2% agar) was used. The intracellular pH dropped down in a denser intact yeast suspension and rose with an increase in the concentration of dehydrated-rehydrated cells. 相似文献
39.
Incorporation of axonally transported glycoproteins into axolemma during nerve regeneration 总被引:14,自引:4,他引:10 下载免费PDF全文
The insertion of axonally transported fucosyl glycoproteins into the axolemma of regenerating nerve sprouts was examined in rat sciatic motor axons at intervals after nerve crush. [(3)H]Fucose was injected into the lumbar ventral horns and the nerves were removed at intervals between 1 and 14 d after labeling. To follow the fate of the “pulse- labeled” glycoproteins, we examined the nerves by correlative radiometric and EM radioautographic approaches. The results showed, first, that rapidly transported [(3)H]fucosyl glycoproteins were inserted into the axolemma of regenerating sprouts as well as parent axons. At 1 d after delivery, in addition to the substantial mobile fraction of radioactivity still undergoing bidirectional transport within the axon, a fraction of label was already associated with the axolemma. Insertion of labeled glycoproteins into the sprout axolemma appeared to occur all along the length of the regenerating sprouts, not just in sprout terminals. Once inserted, labeled glycoproteins did not undergo extensive redistribution, nor did they appear in sprout regions that formed (as a result of continued outgrowth) after their insertion. The amount of radioactivity in the regenerating nerves decreased with time, in part as a result of removal of transported label by retrograde transport. By 7-14 d after labeling, radioautography showed that almost all the remaining radioactivity was associated with axolemma. The regenerating sprouts retained increased amounts of labeled glycoproteins; 7 or 14 d after labeling, the regenerating sprouts had over twice as much of radioactivity as comparable lengths of control nerves or parent axons. One role of fast axonal transport in nerve regeneration is the contribution to the regenerating sprout of glycoproteins inserted into the axolemma; these membrane elements are added both during longitudinal outgrowth and during lateral growth and maturation of the sprout. 相似文献
40.